Dielectric materials have numerous applications in integrated circuitry. For instance, dielectric materials may be incorporated into capacitors, may be utilized as gate dielectric of field effect transistors, may be utilized as intergate dielectric of non-volatile transistors, and may be utilized for electrically isolating adjacent semiconductor components from one another.
The dielectric properties of dielectric materials can be expressed in terms of a dielectric constant. The dielectric constant (k) is the ratio of the permittivity of a substance to the permittivity of free space. It is an expression of the extent to which a material concentrates electric flux. As the dielectric constant increases, the electric flux density increases, if all other factors remain unchanged. Accordingly, a thick layer of a material having a high dielectric constant may be utilized to achieve the same electric flux density as a thin layer of a material having a lower dielectric constant.
There is a continuing goal to increase integration density, and a corresponding goal to reduce the size of individual integrated circuit components. Accordingly, there is interest in utilizing dielectric materials having high dielectric constants in integrated circuitry, in that such materials may increase the electric flux density to compensate for reduced area in order to achieve desired operational properties.
Unfortunately, materials with high dielectric constants tend to break down more easily when subjected to intense electric fields than do materials with low dielectric constants. Also, materials with high dielectric constants tend to have high dielectric dispersion, and slow dielectric relaxation.
Dielectric dispersion (permittivity as a function of frequency) is fundamental to any material system because there are multiple mechanisms that contribute to capacitance at lower frequencies, and which decrease with increasing frequency. If dielectric dispersion is high, the response rate of a dielectric material is more altered by changes in frequency then if the dielectric dispersion is low.
Dielectric relaxation is a parameter utilized to express the dielectric response in the time domain to apply (or remove) electric field (e.g., the rate at which charge is stored or released from a capacitor). If dielectric relaxation is slow, the response time will be long. Materials with high dielectric constants tend to have slower response times than do materials with lower dielectric constants.
One of the uses of dielectric materials is in capacitors of dynamic random access memory (DRAM) unit cells. In such applications, it is desired that the dielectric materials store a large quantity of flux in a small volume, and yet have a rapid response time (i.e., rapidly store or release charge). As discussed above, materials with high dielectric constants may store a large quantity of flux in a small volume, but tend to have relatively slow response times.
It would be desirable to develop dielectric structures that have the desired properties of high dielectric materials, and yet that also have better response times than do materials with high dielectric constants. Such dielectric structures will be useful for capacitors of integrated circuitry for the reasons discussed above, and may also have application for utilization in other components of integrated circuitry, such as, for example, for utilization as gate dielectric and/or for utilization as intergate dielectric.